Transcriptome provides insights into bovine mammary regulatory mechanisms during the lactation cycle

The molecular events underlying the lactation curve of dairy animals have long been a biological conundrum for mammary biologists, and a cause of a considerable loss of income for dairy farmers. To better understand the regulatory mechanisms and developmental processes of the mammary gland during the lactation cycle, whole-genome transcriptome profiles of bovine mammary tissues at five different lactation stages were investigated using the RNA-Seq technique. The differentially expressed genes were identified by comparing different lactation stage combinations. Gene expression changes were validated using quantitative reverse-transcription polymerase chain reaction. Some differentially expressed genes were found to locate in the known quantitative trait loci regions that are associated with multiple milk production traits. Proteins of potentially important genes were confirmed to be expressed in the mammary epithelium of dairy cows. An integrated analysis of differential gene expression indicated that internal development regularities underlying the shape of the milk production curve. First, the mammary gland is enriched in similar activities during lactation onset and involution, but in opposite regulatory directions. Second, the lactation stages before and after the milk peak shared similar biological processes that were mainly involved in extracellular matrix remodelling. The discoveries of the study provide information necessary to improve milk production.